move builds to github actions, update to BUFFERSIZE=20 and OpenBLAS v0.3.13

[mattip]

Things to undo once this works

• move travis to legacy until this is merged
• the upload is without --force to avoid too much churn

[mattip]

There are 15 builds in the new task (3 python versions) * (macOS + macOS,interface64 + linux64,interface64 + linux64 + linux32)

[mattip]

The upload step succeeds, using a --skip directive to not override existing tarballs.

The calculation in the comment above was wrong: there are 5 tarballs needed, the python version does not matter for OpenBLAS. I was getting this PR confused with other ones for MacPython that produce wheels.

But there is are two problems: the interface64 is not appearing in the label and I am not producing manylinux2010 tarballs.

[mattip]

That is better: now there are (manylinux1, manylinux2010, manylinux2014) * (ubuntu_x86, ubuntu_x86_64, ubuntu_x86_64 + interface64) + macOS + macOS + interface64 = 11 jobs

[mattip]

The 0.3.13 tarballs were uploaded for the various x86 platforms. Now to re-enable a more limited travis build.